I have a group of 7th graders who would like to compare a 3 blade fan to fans with other numbers of blades to see which generates the most energy.How can we set up a fan so that we can measure the energy output?

Project Question: I am the science fair supervisor at my school--new to the job. Had a team of 3 7th grade girls who want to compare a 3-blade turbine fan to a 2 and 4-blade fan and see if one type generates more electricity than other. Great idea, they are not sure how to connect a fan to some sort of source to measure the power generated. Do you have an answer? Or perhaps another way they could measure the how well the fans compared to each other that would be useful?

This sounds like a great project. I have seen many of these wind turbine science projects at local science fairs over recent years. They are a lot of fun and can teach the students a lot of things.

Before you set up a system to measure the energy output, you need to spend time working out a way to present the air to the fan turbine in a very consistent manner. The air must be flowing into each test specimen at the same velocity, in the same quantity and STRAIGHT. Straight is the most common thing overlooked in wind turbine experiments. If the wind is generated by placing a fan in front of the turbine, the air coming off the fan is not coming just straight off, but it is spinning as well. This spin will affect the performance of different turbine designs in different ways. So it is important to make sure the flow is straight. This can be done simply by building a simple "egg crate". That is a box that has partitions in it to straighten the flow. If you take a hand full of soda straws, you form a lot of long, slender, straight sections. This will straighten the air flow. A good design rule is to construct this egg crate so the length of each individual cell is 7 times the equivalent diameter of the cell. This will give maximum straightening for the least amount of resistance. This is a principle used in good wind tunnel designs. Here are a couple web sites that demonstrate that:

Once you can provide good, straight air flow to your turbine test pieces, the simplest way to measure the energy output is to connect the turbine to an electric generator. This can be just a small, simple DC motor that you can purchase at most any hobby shop or from a company that specializes in educational supplies. You'll need a "multimeter" to measure the output of the motor, which will operate as a generator. Take the wires coming out of the generator and run them through a small light bulb. Use the multimeter to measure the voltage and the amps coming out of the generator. By multiplying th voltage times the amps, you can determine the power.

I hope this doesn't all sound too complicated. Once you get things set up the experiments should go fairly quickly.

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